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The parents of Kayla Mueller, the American aid worker killed while in ISIS captivity, are “absolutely” certain their daughter’s Syrian boyfriend put his life in danger during an attempted rescue.

“Throughout this whole ordeal, there's very few people that we didn't doubt at some point, very few that we didn't doubt they had some other motive or ulterior motive,” Carl Mueller told TODAY’s Savannah Guthrie in an exclusive interview. “We know he risked his life to try and save her.”

The Muellers said Kayla insisted on going to Syria after her boyfriend, Omar Alkhani, a 33-year-old photographer and activist whom she had known since 2010, was called to help an aid hospital there. The couple agreed to tell people they were married if they ever got captured.